We seek to characterize the interactions between urease apoprotein (Apo) and four accessory proteins that are required for urease activation, UreD, UreE, UreF, and UreG. We have established that three of the auxiliary proteins form the following complexes with Apo: UreD-Apo, UreF-UreD-Apo, and UreG-UreF-UreD-Apo, and plan to analyze the sites of peptide-peptide interaction by a combination of methods including mass spectrometric analysis of crosslinked peptides. In addition, we plan to carry out chemical footprinting studies in which sites of chemical modification on Apo are examined in the presence of the various complexes to deduce which sites are obscured by the accessory proteins.